The present invention relates to systems for medical diagnosis and treatment, and specifically to using reference field transducers and medical probes with probe field transducers to detect the position, orientation, or both of the probe within the body of a subject.
There are many medical procedures in which probes, such as catheters, are introduced into the body of a subject or patient. In procedures such as cardiac catherization and neurosurgery, it is often necessary for the physician or surgeon to know the location of the distal end of the probe inside the body. Although imaging methods such as fluoroscopy and ultrasound are sometimes used for this purpose, they are not always practical or desirable. For example, such systems typically require continuous imaging of the probe and patient during the procedure. In addition, fluoroscopic systems are often undesirable because that they expose the patient and physician to substantial ionizing radiation.
A number of locating systems for detecting the position of a probe or a catheter tip in the body of a patient have been proposed without the need for continuous imaging of the patient. These systems include, for example, those disclosed in U.S. Pat. Nos. 5,558,091; 5,391,199; 5,443,489; and International Patent Publications WO 94/04938 and WO 96/05768, the disclosures of which are hereby incorporated herein by reference. Other electromagnetic tracking systems, not necessarily for medical applications, are described in U.S. Pat. Nos. 3,644,825, 3,868,565, 4,017,858, 4,054,881 and 4,849,692.
Systems such as those disclosed in the ""091, ""199 and ""489 patents and in the ""768 publication determine the disposition (i.e., position, orientation, or both) of a probe using one or more fields transducers, such as a Hall effect devices, magnetoresistive devices, coils or other antennas carried on the probe. The transducers are typically located at or adjacent the distal end of the probe or at a precisely known location relative to the distal end of the probe. Such systems further utilize one or more reference field transducers disposed outside the body to provide an external frame of reference. The reference field transducers are operative to transmit or detect non-ionizing fields or field components such as magnetic field, electromagnetic radiation or acoustical energy such as ultrasonic vibration. By transmitting fields between the external reference field transducers and the probe field transducers, characteristics of the field transmissions between these devices can be determined and then used to determine the position and orientation of the probe in the external frame of reference.
As described, for example, in the aforementioned ""091 patent, the frame of reference of the external field transducers can be registered with the frame of reference of imaging data such as magnetic resonance imaging data, computerized axial tomographic (xe2x80x9cCATxe2x80x9d) data, or conventional x-ray imaging data, and hence the position and/or orientation data derived from the system can be displayed can as a representation of the probe superimposed on an image of the patient""s body. The physician can use this information to guide the probe to the desired location within the patient""s body, and to monitor its location and orientation during treatment or measurement of the internal body structure. This arrangement greatly enhances the ability of the physician to navigate the distal end of the problem through bodily structures and offers significant advantages over conventional methods of navigating probes within the body by feel alone. Because it does not require acquiring an optical image of the surrounding tissues for navigation purposes, it can be used with probes which are too small to accommodate optical elements. These transducer-based systems also avoid the difficulties associated with navigation of a probe by continuous imaging of the probe and patient during the procedure and avoids, for example, prolonged exposure to ionizing radiation inherent in fluoroscopic systems.
Such systems typically utilize reference field transducers or coils which are provided in a fixed, immovable array, in locations such as on the ceiling of an operating room or rigidly fixed to operating or catherization table. In medical applications, where the system is used to track the location of a probe inside the body of a patient, the coil mounting may also interfere with free access by the physician to the patient.
For example, the aforementioned ""768 publication describes a catheter system which uses a plurality of non-concentric coils adjacent to the distal end of the catheter. These coils generate signals in response to externally applied magnetic fields, which allow for the computation of six location and orientation coordinates, so that the disposition of the catheter is known without the need for simultaneous imaging. Preferably, three such coils or radiators are arrayed in fixed locations outside the body, adjacent to the area of the body into which the catheter is introduced. For example, in cardiac catherization, during which the patient is typically supine, three radiators are typically fixedly placed beneath the patient""s thorax, in a fixed coplanar, triangular arrangement, with the centers of the coils from about 2 to 30 cm apart. Undesired movement of this array of radiators, however, can lead to errors in determination of the location or orientation of the catheter.
For detection of the position and orientation of catheters or probes inserted into the brain, the transducers or field radiating coils should desirably be positioned adjacent to the patient""s head. In neurosurgery, however, the patient is often in a seated, upright position or else face-down. Thus, a triangular frame holding the three radiators as described above cannot be comfortably and stably positioned below the head. However, positioning the frame above or beside the head will generally interfere with the surgeon""s manipulation of probes and surgical tools.
It would therefore be desirable to enhance the accuracy and efficacy of probe tracking systems as described above, and other types of systems involving application of electromagnetic or other non-ionizing energy field to a human body, by adjusting and optimizing the positions of the reference field transducers. As in the case of neurosurgery, optimal positioning may not be possible if the transducers are constrained in fixed position by a triangular or other mounting frame. For example, when a probe is to be tracked inside a patient""s abdomen, it may be desirable to place radiators in fixed, known positions around the circumference of the abdomen, rather than under the patient""s back.
In addition, it would be desirable to provide greater flexibility as to where the transducers are placed about the subject. Such increased placement flexibility would allow the physician to have easier access to the patient. Flexibility over placement of the transducers would allow custom positioning of the transducers to move them to the closest possible location to increase sensitivity of the locating system.
The present invention addresses the need of providing greater flexibility in the positioning of position determining transducers by providing a system for determining the disposition of a probe within the body of a patient, comprising a probe having one or more probe field transducers mounted therein and one or more reference field transducers mounted on a frame. The system includes means for mounting the frame for movement relative to the patient so that the reference field transducers can be selectively positioned in different positions in close proximity to the body of the patient. The mounting means may desirably comprise a flexible, goose neck arm.
Transmission means are provided to transmit one or more non-ionizing fields between the probe field transducers and the reference field transducers and detection means detect each such transmitted field. Finally, calculation means determine the relative disposition of said probe with respect to said reference field transducers from properties of the detected fields and from the relative dispositions of said reference field transducers with respect to one another.
In preferred embodiments, two or more reference field transducers are provided and the frame incorporates a linkage so as to allow each of said reference field transducers to be movable in a known spatial relationship with respect to one another.
In other preferred embodiments, translation means, such as one or more fiducial transducers attached to the body of the patient, translate the disposition of said probe relative to said reference field transducers to a known deposition relative to the body of the patient.
In a method in accordance with a preferred embodiment of the present invention, the disposition of a probe within the body of a patient is determined by the steps of: (a) providing a probe having one or more probe field transducers mounted therein; (b) providing one or more reference field transducers mounted on a frame having means for mounting the frame for movement relative to the patient so that the reference field transducers can be selectively positioned in different positions in close proximity to the body of the patient; (c) adjusting the frame so that said reference field transducers are positioned in a first location in close proximity to the body of the patient; (d) transmitting one or more non-ionizing fields between the probe field transducers and the reference field transducers; (e) detecting each such transmitted field; and (f) calculating the relative disposition of the probe with respect to the reference field transducers from properties of the detected fields and from the relative dispositions of the reference field transducers with respect to one another.
In a preferred method, the present invention further includes the step of translating the disposition of the probe relative to the reference field transducers to a known disposition relative to the body of the patient. Preferably, the translation step includes comprises attaching one or more fiducial transducers to the body of the patient and detecting non-ionizing fields transmitted between the reference field transducers and the fiducial transducers.
It is also an object of the present invention to provide a stable frame to hold reference field transducers for use in determining the disposition of a probe inside the body of a subject during a medical or surgical procedure. In one aspect of the present invention, the frame is suitable for positioning the reference field transducers in close proximity to the subject""s head without interfering with neurosurgical procedures.
A further object of the present invention is that the frame may be quickly and conveniently fixed in a desired position for optimal transmission of non-ionizing fields into a part of the subject""s body, preferably surrounding the part of the body, and quickly removed from the position thereafter.
In preferred embodiments of the present invention, apparatus for generating non-ionizing energy fields, useful for determining the disposition of a probe inside the body, comprises two or more reference field transducers fixed to a rigid frame of a shape that allows the transducers to be positioned stably in an optimal location in close proximity to a part of the body into which the probe is inserted, so as to allow accurate determination of the disposition of the probe. In preferred embodiments of the present invention, the reference field transducers are radiator coils which generate electromagnetic fields.
In some preferred embodiments of the present invention, the apparatus for generating non-ionizing fields comprises three transducers or coils fixed to a rigid frame. Preferably the frame is conveniently and stably positioned below the thorax or abdomen during insertion of probes therein. In other preferred embodiments of the present invention, for use in neurosurgery, the apparatus for generating fields comprises three coils fixed to a frame below the head, in close proximity to the head. Preferably the frame includes an opening that is adapted to fit around the head or neck.
More generally, in preferred embodiments of the present invention, three or more co-planar reference field transducers define a polygonal shape, wherein the transducers correspond to the vertices of the polygon. A section of the frame corresponding to the side of the polygon is open, and the frame is positioned so that a part of the body is partly contained in this open section. The frame may comprises a mounting bracket, which couples rigidly to the operating table, bed or other apparatus used for fixing the subject""s position.
In some preferred embodiments of the present invention, the frame couples to apparatus for fixing the position of a subject""s head during neurosurgery. In one such preferred embodiment, one or more reference field transducers are fixed to the head fixing apparatus. Electromagnetic fields generated by the transducers cause them to generate position-responsive electrical signals, which are analyzed in order to determine and verify the position of the apparatus relative to the frame. Furthermore, in some such preferred embodiments of the present invention the frame or the head fixing apparatus further include predetermined, known locations, which are marked on the frame or head fixing apparatus, wherein a probe for insertion into the body is first placed in these locations for calibration and reference positioning.
Additionally, in some preferred embodiments of the present invention, the mounting bracket includes a fixable joint, which allows the angular orientation of the frame relative to the bed or relative to the head fixing apparatus to be adjusted and then rigidly fixed at a desired angle. In some preferred embodiments, the frame comprises one or more adjustment hinges. Each such hinge may be flexed so as to adjust the angle between two sides of the frame adjacent thereto, and then fixed rigidly at the desired angle.
In some preferred embodiments of the present invention, the frame comprises head rest fixtures. The positions of these fixtures may be adjusted so that the fixtures fit snugly against the head, so as to maintain the head in a fixed position relative to the reference field transducers and prevent motion of the head relative to the frame.
There is therefore provided in accordance with a preferred embodiment of the present invention, apparatus for generating non-ionizing fields inside the body of a subject, comprising a plurality of reference field transducers, which generate non-ionizing fields, and a rigid frame to which the transducers are fixed. The rigid frame is constructed so as to allow the reference field transducers to be fixably positioned in close proximity to the body. Preferably, the transducers define a polygon, and the frame is constructed so as to be positionable so that an axis perpendicular to the plane of the polygon and passing through the its center passes through the body. Furthermore, the frame is preferably constructed so as to be positionable so that a part of the body is substantially inside the polygon.
Preferably, the frame includes a mounting bracket, which couples rigidly to an operating table or bed. The mounting bracket preferably includes a fixable joint, which is constructed so as to allow the frame to be adjusted and fixed at a desired angle relative to the operating table or bed. Furthermore, the frame may preferably include a plurality of arms and an adjustment hinge, which couples two or more of the arms and is constructed so as to allow the angle defined by the two or more arms that it couples to be adjusted and fixed rigidly in a desired position.
Preferred embodiments of the present invention provide that the frame be adapted so that the reference field transducers are fixably positioned in close proximity to the head and generate non-ionizing fields in a vicinity of the head. Preferably the frame is mechanically coupled to apparatus for fixing the position of the head during surgery. Alternatively the frame may be adapted to fix the position of the head during surgery. The frame may further comprise head engaging elements, which bear against opposite sides of the head. Preferably, the transducers are coils which generate magnetic fields.
There is further provided in accordance with a preferred embodiment of the present invention, a system for determining the position and orientation of a probe inside the body of a subject, including apparatus for generating fields, as described above; a probe for insertion into the body; and at least one device responsive to the fields for determining position and orientation coordinates of the probe. Preferably, this system includes one or more position sensing devices, preferably fixed to the probe, and adapted so to allow the positions of the transducers to be determined. Preferably the fields are magnetic fields, and the field responsive device is a coil. Also, the frame preferably further includes probe calibration receptacles.
Further preferred embodiments of the present invention include apparatus for generating non-ionizing fields in the vicinity of the head of a human medical patient, which such apparatus includes one or more reference field transducers and a rigid frame to which the transducers are fixed. The frame has an opening therein in which the head can be located such that the frame is in close proximity to and at least partially encircles a portion of the head or neck of the patient.
The frame preferably comprises a pair of arm members defining a triangle having two closed sides and an open side such that a portion of the head or neck can be readily positioned within the frame through the open side. Preferably, transducers are positioned at at least the three corners of the frame and the arm members of the frame are hingedly connected to one another. Further, means for measuring the relative displacement between the arm members can be provided.
In other preferred embodiments, the head clamp may be attached to the frame to prevent movement of the head. In another preferred arrangement, the frame may be integrally formed with a head clamp to prevent movement of the head. In other preferred embodiments, the frame may further include head engaging fixtures adjustable to tighten to the head.